diff --git a/lib/rack/builder.rb b/lib/rack/builder.rb
index db8e2d8eb..40778ce47 100644
--- a/lib/rack/builder.rb
+++ b/lib/rack/builder.rb
@@ -46,13 +46,13 @@ def self.parse_file(config, opts = Server::Options.new)
       return app, options
     end
 
-    def initialize(&block)
-      @ins = []
+    def initialize(default_app = nil,&block)
+      @use, @map, @run = [], nil, default_app
       instance_eval(&block) if block_given?
     end
 
-    def self.app(&block)
-      self.new(&block).to_app
+    def self.app(default_app = nil, &block)
+      self.new(default_app, &block).to_app
     end
 
     # Specifies a middleware to use in a stack.
@@ -75,7 +75,11 @@ def self.app(&block)
     # The +call+ method in this example sets an additional environment key which then can be
     # referenced in the application if required.
     def use(middleware, *args, &block)
-      @ins << lambda { |app| middleware.new(app, *args, &block) }
+      if @map
+        mapping, @map = @map, nil
+        @use << proc { |app| generate_map app, mapping }
+      end
+      @use << proc { |app| middleware.new(app, *args, &block) }
     end
 
     # Takes an argument that is an object that responds to #call and returns a Rack response.
@@ -93,7 +97,7 @@ def use(middleware, *args, &block)
     #
     #   run Heartbeat
     def run(app)
-      @ins << app #lambda { |nothing| app }
+      @run = app
     end
 
     # Creates a route within the application.
@@ -116,22 +120,26 @@ def run(app)
     # This example includes a piece of middleware which will run before requests hit +Heartbeat+.
     #
     def map(path, &block)
-      if @ins.last.kind_of? Hash
-        @ins.last[path] = self.class.new(&block).to_app
-      else
-        @ins << {}
-        map(path, &block)
-      end
+      @map ||= {}
+      @map[path] = block
     end
 
     def to_app
-      @ins[-1] = Rack::URLMap.new(@ins.last)  if Hash === @ins.last
-      inner_app = @ins.last
-      @ins[0...-1].reverse.inject(inner_app) { |a, e| e.call(a) }
+      app = @map ? generate_map(@run, @map) : @run
+      fail "missing run or map statement" unless app
+      @use.reverse.inject(app) { |a,e| e[a] }
     end
 
     def call(env)
       to_app.call(env)
     end
+
+    private
+
+    def generate_map(default_app, mapping)
+      mapped = default_app ? {'/' => default_app} : {}
+      mapping.each { |r,b| mapped[r] = self.class.new(default_app, &b) }
+      URLMap.new(mapped)
+    end
   end
 end
diff --git a/test/spec_builder.rb b/test/spec_builder.rb
index f7501ae42..d3e7261da 100644
--- a/test/spec_builder.rb
+++ b/test/spec_builder.rb
@@ -99,6 +99,26 @@ def self.env
     Rack::MockRequest.new(app).get("/").should.be.server_error
   end
 
+  it "can mix map and run for endpoints" do
+    app = Rack::Builder.app do
+      map('/sub') { run lambda { |inner_env| [200, {}, ['sub']] }}
+      run lambda { |inner_env| [200, {}, ['root']] }
+    end
+
+    Rack::MockRequest.new(app).get("/").body.to_s.should.equal 'root'
+    Rack::MockRequest.new(app).get("/sub").body.to_s.should.equal 'sub'
+  end
+
+  it "accepts middleware-only map blocks" do
+    app = Rack::Builder.app do
+      map('/foo') { use Rack::ShowExceptions }
+      run lambda { |env| raise "bzzzt" }
+    end
+
+    proc { Rack::MockRequest.new(app).get("/") }.should.raise(RuntimeError)
+    Rack::MockRequest.new(app).get("/foo").should.be.server_error
+  end
+
   should "initialize apps once" do
     app = Rack::Builder.new do
       class AppClass
@@ -120,6 +140,23 @@ def call(env)
     Rack::MockRequest.new(app).get("/").should.be.server_error
   end
 
+  it "allows use after run" do
+    app = Rack::Builder.app do
+      run lambda { |env| raise "bzzzt" }
+      use Rack::ShowExceptions
+    end
+
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+    Rack::MockRequest.new(app).get("/").should.be.server_error
+  end
+
+  it 'complains about a missing run' do
+    proc do
+      Rack::Builder.app { use Rack::ShowExceptions }
+    end.should.raise(RuntimeError)
+  end
+
   describe "parse_file" do
     def config_file(name)
       File.join(File.dirname(__FILE__), 'builder', name)